The objective of this proposal is to perform an analysis of Ki-MSV-transformed mouse cells in relation to the following factors which affect the expression of the viral genome: a) Integration site, orientation and representation of the viral genome DNA in host cell DNA; b) Initiation site, and processing of viral transcripts from viral and/or host DNA; c) Possible identification of the Ki-MSV mRNA which codes for proteins responsible for cellular transformation. The methods employed are: 1) Preparation of specific probes which detect specific loci of the Ki-MSV genome; 2) reassociation kinetics to quantitate virus-related sequences; 3) restriction enzymes and the filter transfer technique to analyze viral DNA in relation to host DNA; 4) S-1 nuclease mapping of Ki-MSV mRNA; and 5) nucleotide sequencing of Ki-MSV DNA. The information obtained by this approach will lead to a better understanding of the mechanisms of cellular and viral control of transformation.